In conventional practice, microphone units comprising a function for converting inputted sounds to electrical signals and outputting the signals have been applied to various types of voice input devices (for example, mobile telephones, transceivers, and other voice communication devices; voice recognition systems and other information processing systems that use techniques for analyzing inputted voices; audio recording devices; and the like). While a need arises for such microphone units that suppress background noise and pick up only proximal sounds, there is also a demand for such microphone units that pick up not only proximal sounds but distant sounds as well.
A mobile telephone is described hereinbelow as an example of a voice input device comprising a microphone unit. When the mobile telephone is used to make a call, usually the user holds the mobile telephone in their hand and uses the telephone with their mouth near a microphone portion. Therefore, a need commonly arises for the microphone provided to the mobile telephone to have a function for suppressing background noise and picking up only proximal sounds (a function as a close-talking microphone).
However, recent mobile telephones are provided with a hands-free function so that a call can be made while driving an automobile without holding the telephone in hand, for example, and are provided with a function for recording video. In cases in which a mobile telephone is used with the hands-free function, since the position of the mouth of the user is a position separated from the mobile telephone, a need arises that the microphone have a function for picking up not only proximal sounds but distant sounds as well. There is also a need for the microphone to have a function for picking up not only proximal sounds but distant sounds as well also in cases of recording video, because there must be audio recording for the surrounding area when the video is recorded.
Specifically, due to mobile telephones becoming multifunctional in recent years, a need arises for both a function for suppressing background noise and picking up only proximal sounds, and a function for picking up not only proximal sounds but distant sounds as well. To adapt to such a demand, one possibility is to separately install a microphone unit comprising a function as a close-talking microphone, and an omnidirectional microphone unit capable of also picking up distant sounds.
Another possible method is to apply the microphone unit disclosed in Patent Literature 1, for example, to a mobile telephone. The microphone unit disclosed in Patent Literature 1 is designed so that one of two open parts for inputting voice is switched between an open state and a closed state by an opening and closing mechanism. The microphone unit disclosed in Patent Literature 1 functions as a bidirectional differential microphone when the two open parts are open, and functions as an omnidirectional microphone when one of the two open parts is closed.
When the microphone unit functions as a bidirectional differential microphone, it is applied to cases in which the user uses the mobile telephone in hand because the microphone unit can suppress background noise and pick up only proximal sounds. When the microphone unit functions as an omnidirectional microphone, it is applied to cases in which the hands-free function or the video record function is used because it can pick up distant sounds as well.